a b/Segmentation/model/backbone.py
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import tensorflow as tf
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import tensorflow.keras.layers as tfkl
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from tensorflow.keras.applications import VGG16, VGG19
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from tensorflow.keras.applications import ResNet50, ResNet50V2, ResNet101, ResNet101V2, ResNet152, ResNet152V2
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from tensorflow.keras.models import Model
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class Encoder(object):
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    def __init__(self,
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                 weights_init,
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                 model_architecture='vgg16'):
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        self.weights_init = weights_init
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        if model_architecture == 'vgg16':
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            self.model = VGG16(weights=self.weights_init, include_top=False)
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            self.bridge_list = [2, 5, 9, 13, 17]
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        elif model_architecture == 'vgg19':
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            self.model = VGG19(weights=self.weights_init, include_top=False)
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            self.bridge_list = [2, 5, 10, 15, 20]
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        elif model_architecture == 'resnet50':
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            self.model = ResNet50(weights=self.weights_init, include_top=False)
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            self.bridge_list = [4, 38, 80, 142, -1]
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        elif model_architecture == 'resnet50v2':
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            self.model = ResNet50V2(weights=self.weights_init, include_top=False)
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            self.bridge_list = [2, 27, 62, 108, -1] 
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        elif model_architecture == 'resnet101':
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            self.model = ResNet101(weghts=self.weights_init, include_top=False)
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            self.bridge_list = [4, 38, 80, 312, -1]
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        elif model_architecture == 'resnet101v2':
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            self.model = ResNet101V2(weights=self.weights_init, include_top=False)
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            self.bridge_list = [2, 27, 62, 328, -1]
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        elif model_architecture == 'resnet152':
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            self.model = ResNet152(weights=self.weights_init, include_top=False)
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            self.bridge_list = [4, 38, 120, 482, -1]
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        elif model_architecture == 'resnet152v2':
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            self.model = ResNet152V2(weights=self.weights_init, include_top=False)
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            self.bridge_list = [2, 27, 117, 515, -1]
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    def construct_backbone(self):
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        output_list = []
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        for _, layer_idx in enumerate(self.bridge_list):
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            layer_output = self.model.layers[layer_idx].output
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            output_list.append(layer_output)
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        backbone = Model(inputs=self.model.input, outputs=output_list)
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        return backbone
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    def freeze_pretrained_layers(self):
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        for layer in self.model.layers:
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            layer.trainable = False